Structural and magnetic properties of bulk and thin films of Mg0.95Mn0.05Fe2O4

샤런드라쿠마르,S.K. Sharma,Alimuddin,이찬규,B.H. Koo,M. Knobel,R.J. Choudhary,Ravi Kumar 한국물리학회 2009 Current Applied Physics Vol.9 No.5

We present here a comparative study on structural and magnetic properties of bulk and thin films of Mg0.95Mn0.05Fe2O4 ferrite deposited on two different substrates using X-ray diffraction (XRD) and dc magnetization measurements. XRD pattern indicates that the bulk sample and their thin films exhibit a polycrystalline single phase cubic spinel structure. It is found that the film deposited on indium tin oxide coated glass (ITO) substrate has smaller grain size than the film deposited on platinum coated silicon (Pt–Si) substrate. Study of magnetization hysteresis loop measurements infer that the bulk sample of Mg0.95Mn0.05Fe2O4 and its thin film deposited on Pt–Si substrate shows a well-defined hysteresis loop at room temperature, which reflects its ferrimagnetic behavior. However, the film deposited on ITO does not show any hysteresis, which reflects its superparamagnetic behavior at room temperature.

Ferromagnetism in Chemically-synthesized Co-doped ZnO

샤런드라쿠마르,Y. J. Kim,B. H. Koo,최희규,이찬규,S. K. Sharma,M. Knobel,S. Gautam,K. H. Chae 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3

We report room temperature ferromagnetism (RTFM) in Co-doped ZnO (Zn1−xCoxO; x = 0.01 − 0.05) powder synthesized using a co-precipitation method. Our magnetometry data reveal a weak FM behavior at RT in the range 0.01 < x < 0.05. FM by magnetic FM moment steadily decreases with increasing dopant. The O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra indicate that O vacancies increases with increasing Co concentration and that the sample with x ≥ 0.03 has more broadening at 535 and 540 eV, which may be due to the oxygen vacancies. Co in the ZnO host reveals a +2 oxidation state via the K edge NEXAFS spectra.

Effect of NiFe2O4 Doping on the Structure, Magnetic Properties and Electrical Properties of La0.7Ca0.3MnO3

김근우,샤런드라쿠마르,서용준,Kai Wang,이찬규,구본흔 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.5

The (La0.7Ca0.3MnO3)1x/(NiFe2O4)x (x = 0 to 0.09) composites were prepared using a conventional solid state reaction method. The structural, magnetic properties, and electrical properties of LCMO/NFO composites were investigated using X-ray diffraction, scanning electron microscopy, field cooled DC magnetization, and magnetoresistance (MR) measurements. The resistivity measured as a function temperature demonstrates that the pure LCMO and x = 0.01 samples display metal to semiconductor transitions. However, the composites of x > 0.03 samples clearly present the electrical behavior as an insulator/semiconductor type behavior. It was observed that the resistivity of the samples increased systemically with an increase of the NFO content. From the MR measurements, it was found that the MR effect is enhanced for x = 0.01 with a NFO composition. In all, the spin-polarized tunneling and the spin-dependent scattering may be beneficial for an improved lowfield magnetoresistance effect. These phenomena can be explained by the segregation of a new phase related to NFO at the grain boundaries or surfaces of the LCMO grains.

Room-temperature Ferromagnetism in Cu-doped ZnO Nanorods Prepared Using a Microwave Irradiation Method

Faheem Ahmed,샤런드라쿠마르,Nishat Arshi,M. S. Anwar,허시내,김근우,여준청,구본흔,Hoa Hong Nguyen 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10

We report the observation of room temperature ferromagnetism in Cu-doped ZnO nanorods prepared by microwave irradiation technique. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that Cu-doped ZnO comprise a single phase nature with wurtzite structure and Cu ions were successfully incorporated into the lattice position of Zn ions in ZnO matrix. Field emission scanning electron microscopy (FESEM) and TEM micrographs suggested that the size of Cu-doped ZnO nanorods ranges from 50 to 70 nm in diameter and 300 to 400 nm in length, respectively. The selected area electron diffraction (SAED) pattern infer that the Cu-ZnO nanorods have single phase nature with preferentially growth direction along [0 0 1] plane. Raman scattering spectra of Cu-doped ZnO nanorods revealed the blue shift of <I>E<SUB>2</SUB></I><SUP>high</SUP> mode that is related to the vibration of oxygen atoms in wurtzite ZnO, suggested the successful doping of Cu at Zn site into ZnO. Magnetization measurements showed that the nanorods exhibit room temperature ferromagnetism.

Finite size effect and influence of temperature on electrical properties of nanocrystalline Ni–Cd ferrites

Khalid Mujasam Batoo,이찬규,샤런드라쿠마르,Alimuddin 한국물리학회 2009 Current Applied Physics Vol.9 No.5

Electrical conductivity and dielectric measurements have been investigated for four different average grain sizes ranging from 3 to 7 nm of nanocrystalline Ni0.2Cd0.3Fe2.5-xAlxO4 (0.0 ≼ x ≼ 0.5) ferrites. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of the Al doped Ni–Cd ferrites. The analysis of data shows only one semi-circle corresponding to the grain boundary volume suggesting that the conduction mechanism takes place predominantly through grain boundary volume in the studied samples. The variation of impedance properties with temperature and composition has been studied in the frequency range of 120 Hz–5 MHz between the temperatures 300–473 K. The hopping of electrons between Fe3+ and Fe2+ as well as hole hopping between Ni3+ and Ni2+ ions at octahedral sites are found to be responsible for conduction mechanism. The dielectric constant and loss tangent (tand) are found to decrease with increasing frequency, whereas they increase with increasing temperature. The dielectric constant shows an anomalous behavior at selected frequencies, while the temperature increases, which is expected due to the generation of more electrons and holes as the temperature increases. The behavior has been explained in the light of Rezlescu model.

Influence of the thickness on structuralmagnetic and electrical properties of La0.7Ca0.3MnO3 thin film

Young Joo Kim,샤런드라쿠마르,이찬규,구본흔,정준기,김원정 한국물리학회 2010 Current Applied Physics Vol.10 No.3

We have studied the effect of thickness on the structural, magnetic and electrical properties of La0.7Ca0.3MnO3 thin films prepared by pulsed laser deposition method using X-ray diffraction, electrical transport, magneto-transport and dc magnetization. X-ray diffraction pattern reflects that all films have c-axis epitaxial growth on LaAlO3 substrate. The decrease in out-of-plane cell parameter specifies a progressive relaxation of in the plane compressive strain as the film thickness is increases. From the dc magnetization measurements, it is observed that ferromagnetic to paramagnetic transition temperature increases with increase in the film thickness. Magneto-resistance and temperature coefficient of resistance increases with film thickness and have maximum value near its metal to insulator transition temperature.

A comparative study of particle size analysis in fine powder: The effect of a polycomponent particulate system

최희규,Woong Lee,김동욱,샤런드라쿠마르,Jonghak Ha,Seongsoo Kim,Jungeun Lee 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.1

We report the particle size distribution of poly component particulate systems studied in three kinds of experimental methods. Six analyzers, such as Mastersizer Microplus (Malvern Instruments Ltd., UK), LS230 (Coulter Electronics Ltd., USA) LMS30 (Seishin, Japan), Analysette22 (Fritsch, Germany), HELOS (Sympatec, Germany) based on a laser diffraction and scattering method, and the SKC-2000S (Seishin Co., Ltd., Japan) based on the centrifugal sedimentation method, were used to study the particle size distribution. The results do not show reasonably good agreement between the different analyzers and different sample systems. There is a discrepancy regarding the absolute values, which can be explained by the fact the techniques used are based on different measuring principles. The results of the present study reflect that the investigator must carefully select the particle size analyzer for a particular application. Therefore, we suggest that it is necessary to measure the particle size distribution by using at least two types of analyzers or more of different makers.

Influence of Al doping on electrical properties of Ni–Cd nano ferrites

Khalid Mujasam Batoo,샤런드라쿠마르,이찬규,Alimuddin 한국물리학회 2009 Current Applied Physics Vol.9 No.4

We have reported the structural and electrical properties of nano particles of Al doped Ni0.2Cd0.3Fe2.5O4 ferrite using X-ray diffraction, dielectric spectroscopy and impedance spectroscopy at room temperature. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure. The average particle size estimated using Scherrer formula for Lorentzian peak (311), has been found 5(±) nm. The results obtained show that real (ε'), imaginary (ε'') part of the dielectric constant, loss tangent (tanδ), and ac conductivity (σac) shows normal behaviour with frequency. The dielectric properties and ac conductivity in the samples have been explained on the basis of space charge polarization according to Maxwell–Wagner two-layer model and the Koop’s phenomenological theory. The impedance analysis shows that the value of grain boundary impedance increases with Al doping. The complex impedance spectra of nano particles of Al doped Ni–Cd ferrite have been analyzed and explained using the Cole–Cole expression.

Above room temperature magnetic transition and magnetocaloric effect in La_0.66_Sr_0.34_MnO₃

M. S. Anwar,샤런드라쿠마르,Faheem Ahmed,Nishat Arshi,김근우,구본흔 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10

In this study, the magnetic and the magnetocaloric properties of the La0.66Sr0.34MnO3 (LSMO) compound were investigated. The X-ray diffraction result indicates that the LSMO sample has a single phase of rhombohedral symmetry without any impurity phase. The magnetic study reveals that the specimen La0.66Sr0.34MnO3 exhibits a ferromagnetic-paramagnetic transition at TC ∼ 376 K. Using Arrott plots, the phase transition from ferromagnetic to paramagnetic is found to be of second order. A maximum magnetic entropy change of 1.25 J/kgK has been observed for a low applied magnetic field of 1T. The relative cooling power values exhibit a nearly linear dependence on the applied magnetic field. Moreover, the analysis of the magnetocaloric effect (MCE) using the Landau theory o f phase transitions shows good agreement with the experimental results, confirming the importance of magnetoelastic coupling and electron interactions in the magnetocaloric properties of perovskite manganites. This investigation suggests that La0.66Sr0.34MnO3 can be used as a potential magnetic refrigeration material.

Study of dielectric and ac impedance properties of Ti doped Mn ferrites

Khalid Mujasam Batoo,샤런드라쿠마르,이찬규,Alimuddin 한국물리학회 2009 Current Applied Physics Vol.9 No.6

We have reported dielectric and ac impedance properties of Ti doped Mn1+xFe2-2xO4 (0 ≼ x ≼ 0:5) ferrites prepared by solid-state reaction method, using dielectric and impedance spectroscopy in the frequency range of 42 Hz–5 MHz, between the temperatures (300K–473K). The dielectric constant and dielectric loss (tand) decreases with increasing frequency but these parameters increase with increasing temperature. The dielectric loss tangent curves exhibit dielectric relaxation peaks at high frequencies (3.6 kHz– 5 MHz), which are attributed to the coincidence of the frequency of charge hopping between the localized charge states and the external field. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell–Wagner’s two-layer model and the hopping of charge between Fe2+ and Fe3+ as well as between Mn3+ and Mn2+ ions at B-sites. The complex impedance analysis has been used to separate grain and grain boundary in studied samples. Two semicircles corresponding to grain and grain boundary have been observed at low temperature, while only one semicircle has been seen at high temperatures. The resistance of grain and grain boundary both increase with Ti4+ doping.